Osmosis process

ABSTRACT

OSMOSIS PROCESS UTILIZING AS THE SEMIPERMEABLE MEMBRANE, A BLEND OF AT LEAST TWO SYNTHETIC POLYAMIDES SELECTED FROM THE GROUP CONSISTING OF POLY(PIPERAZINISOPHTHALAMIDE), POLY-(TRANS - 2,5- DIMETHYL PIPERAZINTEREPHTHALAMIDE (AND POLY-(TRANS-2,5 -DIMETHYL PIPERAZIN-TRANS-TRANSMUCONAMIDE) OR A BLEND OF AT LEAST ONE SYNTHETIC POLYAMIDE SELECTED FROM THE GROUP CONSISTING OF POLY(PIPERAZINISOPHTHALAMIDE), POLY-(TRANS-2,5-DIMETHYL PIPERAZINTEREPHTHALAMIDE), AND POLY-(TRANS-2,5-DIMETHYL PIPERAZINTRANS-TRANS-MUCONAMIDE), AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF NYLON 6, NYLON 4, NYLON 6.6 AND NYLON 6.10.

United States Patent O M 3,743,597 OSMOSIS PROCESS Lino Credali,Bologna, and Paolo Parrini, Novara, Italy, assignors to ConsiglioNazionale Delle Recherche and Montecatini Edison S.p.A., both of Milan,Italy No Drawing. Original application July 6, 1970, Ser. No. 52,748,now Patent No. 3,693,031. Divided and this application June 26, 1972,Ser. No. 266,461

Claims priority, application Italy, July 8, 1969, 19,318/69 Int. Cl.B0111 13/00 US. Cl. 210-23 2 Claims ABSTRACT OF THE DISCLOSURE Osmosisprocess utilizing as the semipermeable membrane, a blend of at least twosynthetic polyamides selected from the group consisting ofpoly(piperazinisophthalamide), poly-(trans 2,5 dimethylpiperazinterephthalamide (and poly-(trans-2,5-dimethylpiperazin-trans-transmuconamide) or a blend of at least one syntheticpolyamide selected from the group consisting ofpoly(piperazinisophthalamide), poly-(trans-2,5-dimethylpiperazinterephthalamide), and poly-(trans-2,5-dimethylpiperazintrans-trans-muconamide), and a member selected from the groupconsisting of nylon 6, nylon 4, nylon 6.6 and nylon 6.10.

CROSS REFERENCE TO RELATED APPLICATIONS This is a division of copendingapplication Ser. No. 52,748, filed July 6, 1970, now US. Pat. No.3,696,031, issued on Oct. 3, 1972.

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention relates to the use, in reverse osmosis processes, of polymericmaterials which have not heretofore been employed. More particularly,this invention relates to the use of formed articles made of suchpolymeric materials, these materials having a high permeability to waterand being capable of rejecting salts dissolved therein, assemi-permeable membranes in reverse osmosis processes for thedesalinization of waters, such as brackish water, sea water, and otherwaters having various concentrations of dissolved inorganic salts.

(2) Description of the prior art As is Well known, the desalinization(demineralization) of saline waters by means of a reverse osmosisprocess (sometimes also described as ultra-filtering), requires the useof high pressures and selective membranes which are capable ofpermitting pure water to pass therethrough while rejecting or preventingpassage of salts dissolved in said waters.

According to this process, saline water is pushed against the membraneby applying a hydraulic pressure greater than the osmostic pressure ofthe saline solution being treated. A flow of water thereby occurs due tothe difference in hydraulic pressure applied to the two opposite sidesof the membrane, said flow being in a direction opposite to thedirection normally observed in direct osmosis, where the fiow is due toa concentration gradient of the solute on opposite sides of themembrane. Under these conditions, the solution which has passed acrossthe membrane has a greatly reduced saline content.

The water output rate and the degree of demineralization depend onvarious parameters of the process as well as on the properties of thesemi-permeable membrane, such as for instance:

3,743,597 Patented July 3, 1973 Membranes of the conventional type usedfor reverse osmosis processes are generally made of special celluloseesters which possess selective properties, since they are permeable tothe solvents but not to the solutes. More particularly, a polymericmaterial is selective towards a certain solute when a thick andhomogeneous film of such material lets the solvent pass therethrough anddoes not permit passage of the solute. Homogeneous films of celluloseesters, in fact, exhibit the property of being permeable to water whilerepelling salts dissolved therein.

The quantity of solvent which passes tthrough the film depends, allother conditions remaining the same, on the thickness of the homogeneousfilm.

Membranes of the known type, based on cellulose esters and having aparticular physical structure, permit a good flow of the Watertherethrough with a saline rejection of greater than Such membranes aregenerally formed by a relatively thick and homogeneous upper layer and aporous substructure.

Methods for the preparation of such membranes and their use indesalinization processes by reverse osmosis have been described in manypatents and publications. See, e.g., :U.S. Pats. 3,133,132; 3,133,137;3,170,867; 3,283,042; 3,285,765; 3,250,701; 3,290,286; and French Pats.1,510,749 and 1,528,016.

Unfortunately, however, the use of membranes based on cellulose estersin reverse osmosis processes results in a number of difiiculties anddrawbacks. For instance, these polymeric materials do not possess asufliciently high chemical resistance and, in particular, are not veryresistant to hydrolysis by the saline solutions to be puriified. Also,such polymeric materials are rather sensitive to varations in pH.Moreover, such polymeric materials are characterized by a low thermalstability, so that it is possible to use them only at relatively lowoperational temperatures, that is, at temperatures close to roomtemperature, to thereby avoid the occurrence of chemical modificationsin their structure. Additionally, such polymeric materials possess onlya relatively low resistance to bacterial degradation, and further have alow resistance to mechanical compression. Finally, cellulose has a lowpermeability to water. For this reason, in order to obtain high flows ofdeasalinized water (for surface unit and for time unit), it is necessaryto use films or membranes with an active desalinizing layer having athickness generally less than 0.2 micron.

SUMMARY OF THE INVENTION The present invention provides polymericmaterials, in the form of shaped articles such as films, membranes,porous supports, hollow fibers and the like, for use in reverse osmosisseparation and concentration processes. These materials obviate theforegoing difliculties and drawbacks related to the use of materialsbased on cellulose esters.

We use, in reverse osmosis separation and concentration processes,formed articles, such as films, membranes,

porous supports, hollow fibers and the like, which comprise syntheticmaterials having a polyamide structure. The polyamide structure isobtained by reacting piperazine or a substituted derivative thereof witha dicarboxylic aliphatic, cycloaliphatic, or aromatic acid. Thepolyamide structure is characterized by the structural unit of Formula Ii. n .i (1) wherein -CO-X-CO- is a radical derived from any dicarboxylicacid capable of yielding a polyamide, by reaction with a piperazine,With X being a divalent radical, for instance, an alkylene, alkenylene,alkadienylene, arylene, or cycloalkylene radical, or being altogetherabsent (zero) as in the base of oxalic acid; n is either zero or a wholenumber from 1 to 8; and R is a substituent such as alkyl, e.g., ethyl ormethyl; cycloalkyl; alkoxy; aryl; aryloxy; arylalkoxy; or halogen. Thepreparation of such polyamides is described, for example, in US. Pat.2,913,433.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The piperazines used to formthe foregoing polymeric materials have the structure defined in FormulaII HN /NH n (II) wherein n is either zero or a Whole number from 1 to 8;and R is a substituent such as alkyl, e.g., ethyl or methyl; cycloalkyl;alkoxy; aryl; aryloxy; arylalkoxy; or halogen. The substituent R groups,when present in the piperazine ring in a number greater than 1, may bearranged in any steric position whatsoever with respect to the ring.Thus, it is to be understood that Formula II includes pure stereoisomers(cis and trans) as well as mixtures thereof.

Specific examples of piperazines for use in forming the polymericmaterials include piperazine; mono-, di-, triand tetra-methylpiperazines and the corresponding ethyl-piperazines; penta-, hexa-,hepta-, and octamethylpiperazines; 2,3,5 tri n butylpiperazine; 2,3,5,6-tetraphenyl-piperazine; 2 phenyl-piperazine; 2,5 dinaphthylpiperazine;2,2,3,5,5,6 hexaethylpiperazine; phenylmethylpiperazine;propylpiperazine, butylpiperazine; pentylpiperazine; 2,5diphenylpiperazine; 2,6 dipropylpiperazine; 2,5 di n butylpiperazine;2,3,5-tripropylpiperazine; 2,3,5,6 tetra n propylpiperazine;2,5-divinylpiperazine; etc.

Specific examples of dicarboxylic acids that may be used to form thepolypiperazinamides include:

Oxalic acid, adipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid, trans-trans-mueonic acid, terephthalic acid, cishexahydroterephthalic acid, trans-hexahydro terephthalic acid, isophthalic acid,cis-hexahydro isophthalic acid, trans-hexahydro isophthalic acid,phthalic acid, trans-hexahydro-phthalic acid, dibenzoic acid,cis-hexahydro-dibenzoic acid, trans-hexahydro-dibenzoic acid,cis-cis-dodecahydro-dibenzoic acid, cis-trans-dodecahydro-dibenzoicacid, trans-trans-dodecahydro-dibenzoic acid, cis 1,3cyclopentandicarboxylic acid, trans-1,3- cyclopentandicarboxylic acid,trans 1,2 cyclopentandicarboxylic acid, trans 1,2 cyclobutandicarboxylicacid, cis 1,3 cyclobutandicarboxylic acid, trans 1,3cyclobutandicarboxylic acid, trans 1,2 cyclopropandicarboxylic acid, andthe like.

Specific examples of the resultant polymeric materials include:

Poly(piperazinisophthalamide), poly(trans 2,5dimethylpiperazinterephthalamide), poly(trans 2,5dimethylpiperazinadipamide), oly(trans 2,5dimethylpiperazinisophthalamide), poly(trans 2,5dimethylpiperazin-trans-trans-muconamide), etc. More generally, all thepolymeric materials cited in Condensation Polymers by Interfacial andSolution Methods, P. W. Morgan, Interscience Publishers, New York, 1965,pp. 176-179, Table V-lD, would be suitable.

Furthermore, polymeric materials formed of blends of the polyamides ofthe above-mentioned type, or of blends of polyamides of theabove-mentioned type and polyamides having a structure not containingthe piperazine unit, such as, for instance, nylon 6; nylon 4; nylon 6.6;nylon 6.10; and the like may also be advantageously used.

The polymeric material which we use in reverse osmosis separation andconcentration processes have a chemical structure which is completelydiiferent from that of the polymers heretofore used, and may be readilyformed into films, membranes or other shapes suitable for use in reverseosmosis processes.

These polymeric materials, in general, are soluble in common solventssuch as, for example, phenol, m-cresol, 2-chloroethanol,chloroform/methanol mixtures, formic acid, and also strong acids such asconcentrated sulfuric acid, trifluoroacetic acid, and the like.

Certain of these polymers have a melting or softening point sufficientlyhigh to permit their transformation into shaped bodies. From solutionsthereof, by means of a heat-forming process, according to conventionalmethods, with or without the addition of special substances such aswater, methanol, magnesium perchlorate, perchloric acid, maleic acid,formamide, dimethylformamide and the like, it is possible to obtainfilms, membranes or other formed bodies having physical shapes suitablefor use in reverse osmosis processes. The physical form of suchmembranes, obtained according to conventional methods, is of flatconfiguration, due to the relative ease of forming. Sometimes themembranes may also be used in tubular shape or also as hollow fibers.

According to a preferred operational method, membranes for use inreverse osmosis processes may be conveniently prepared by bondingultra-thin polymeric films, comprising polymeric materials of the abovedescribed type and thus capable of rejecting salts, with poroussubstrates which act as supports for the films themselves. These poroussupports, which possess a very high permeability, may be formed from apolymeric material of the same nature as that of the selectivelypermeable film, or may be made from completely different materials.

We have found that when a film or membrane made of the above describedpolymeric materials is placed into a reverse osmosis cell and a salinesolution is pushed against the film or membrane, at a pressure greaterthan the osmotic pressure of the solution, an aqueous solution that isconsiderably enriched in soft (demineralized) water will be obtained.

The desalinization capacity (expressed as percentage of salinerejection) of the films or membranes comprising the polymeric materialsof the above indicated type, may vary from 1 to more than 99%. Thiscapacity canbe greater than 98% for chlorides and greater than 99% forsulfates and carbonates.

Moreover, films and membranes made of the above indicated polymericmaterials are characterized by an intrinsic permeability to water whichis very high and is surprisingly superior to the permeability of filmsor membranes of the known cellulose acetate type (with an acetyl groupcontent of 38.9% with respect to the weight of the cellulose).

The higher permeability to water of the polymeric materials used inaccordance with the present invention is evidenced by the higher valuesof permeability to water for completely dry films, this permeabilitybeing calculated according to the method of Lonsdale, Merten and Rileyin Journal of Applied Polymer Science 9, 1341, (1965). This propertyenables one to achieve surprisingly 3,743,597 6 high flow rates ofproduced water. Production rates may (A) Preparation of completely dryfilms for reverse easily exceed 400 liters per day per square meter offilm osmosis surface when the thickness of the relatively thick,homogeneous surface layer is between 0.2 and 3 microns.

The polymeric materials described above, in the form of shaped articlessuch as films, membranes, porous supports, hollow fibers and the like,are characterized by high chemical resistance and, in particular, areresistant to hydrolysis, are insensitive to variations in pH, and arethermally stable over a wide range of temperatures.

The films, membranes and porous supports wholly or partially made up ofthese polymeric materials are mechanically resistant, tough andflexible, both when dry and when in the moist state, and may be usedover a wide range of temperatures, even temperatures exceeding 100 C.,without the occurrence of any chemical changes in their structure.

The polymeric materials of the above indicated type and in the abovespecified shapes may be used in reverse osmosis processes for thedemineralizzattion of saline waters, and for obtaining potable water(with a total solids content lower than 500 ppm.) from brackish waterand sea water, according to single or multi-stage processes.

Although our description of the use of the membranes, films, poroussupports, hollow fibers and the like comprising polymeric materials ofthe above mentioned type has primarily concerned demineralization ofsaline waters, it is to be understood that these materials may be usedequally well in all other separation processes to which the principle ofreverse osmosis may be applied. Examples of such other processes are:treatment and purification of industrial waters; purification andpotabilization (B) Use of the completely dry films in the desalinationof polluted waters; concentration and recovery of various of SalineSolutions chemical compounds such as chlorides, sulfates, borates,carbonates, nitrates, fertilizers, glutamates, tannins; con- 35 Thefilms prepared as described in paragraph A above The films of polymericmaterials were prepared from solutions of the polymer in a suitablesolvent. The concentration of the polymer in the solution was between 5%and by weight. Either formic acid or a chloroform/ methanol mixture (ina weight ratio of 88/12) was used as the solvent.

The de-aerated homogeneous solution was spread over 10 a glass plate bymeans of a film-spreader. The thus formed films were permitted to dry at30 C. for several hours, until complete evaporation of the solvent hadoccurred. Thereafter, the films were removed from the glass plate, andthey were then tough, transparent and homogeneous. By regulating thethickness of the film-spreader and the concentration of the solution, itwas possible to obtain films with a final thickness between 6 and 100microns. Films with a thickness below 6 microns were prepared byimmersing a glass plate vertically into the polymer solution. This glassplate remained in the solution for at least 10 minutes. It wasvertically extracted from the solution at a speed of about 0.5 cm./sec.The glass plate was then placed horizontally to rest for a few hours at30 C., until complete evaporation of the solvent had occurred. Then theglass plate was immersed into water so as to allow detachment andflotation of the film.

By regulating the speed of extraction of the glass plate from thesolution and the concentration of the solution itself, it was possibleto obtain films with thickness varying from 0.2 to 6 microns.

centration of foodstuffs such as citrus juices, tomato Were P into aStandard ype erse Osmosis cell. An juice, preserves and fruit juices ingeneral, sugar solutions, aqueous saline solution containing 5000p.p.rn. of NaCl milk, tea and coffee extracts; separation of azeotropicwas used as the feed. The linear [flow rate of the feed products;separation and concentration of biological and solution to the surfaceof the film was 100 cm./sec., and pharmaceutical products such ashormones, proteins, vitathe pressure was between 50 and 80 atmospheres.

mins, antibiotics, vaccines, aminoacids and the like, and In Table l thedata and results are given.

all other separation and concentration processes in which The values ofpermeability to water, P (in gr./cm. the reverse osmosis principle maybe used. see), were calculated from the flux and saline rejection Thefollowing examples will further illustrate our invalues according to themethod or" Lonsdale, Merten & vention. All parts are by weight unlessotherwise stated. Riley (J. Appl. Polymer Sci. 9, 1341 (1965)).

TABLE 1 Osmotic properties of completely dry films (teed contained 5,000p.p.m. of NaCl) Pnzo Salt conpermea Flow of tent of ability to Flow ofPressure water water Saline water water 1 Solvent for Thickness (atmos(liters/ (ppm. of rejection, (gr./cm. (liters/day Type of membranepreparing film (microns) pheres) day/ma) NaOl) percent see.) day/m Poly(piperazinisophthalamide) 70 80 2. 34 40 99. 2 3. 5X10 164 Do 36 80 5.98. 6 4. 3X10- 193 Do. 9 26. 5 80 98. 4 5.1)(10- 238 Do 70 50 2. 16 98.3 5. 4X10- 151 Poly (trans-2,5dimethylpiperazinterephthalamide) HCOOH 2850 5. 0 270 94. 6 5. 0X10- Poly(trans-2,5dimethylpiperazinisophthalamide) CH Cla/CHsOH 4O 50 3. 5 1,750 65. 0 4. 9X10- 140 Poly(trans-2,5dimethylpiperazinadipamide) HCOOH60 80 3. 9 950 81. 0 5. 0X10- 234 Poly(trans-2,5dimethylpiperazin,trans-trans muconamidc) HCOOH 24 50 11.5 75584. 9 9. 9X10- 276 Cellulose Acetate 2 Acetone 40 50 1. 55 76 98. 4 2.2X10- 62 D do 40 80 2. 42 70 98. 6 2. 1X10- 97 1 Determined for film ofunitary thickness. 1 Cellulose Acetate Eastman 398-3 (Trademark ofEastman Kodak Chem. Co., U.S.A.).

EXAMPLE 1 The foregoing data, obtained with completely dry films,

show that the permeability to water of the films of this This exampledemonstrates that the polymeric mat rlals 70 invention is very high andis distinctly superior to that of used in accordance with the inventionhave a high permea film of ellulo e acetate obtained by casting a 20%ability to water. and that their use in a process f the solution ofEastman 398-3 cellulose acetate (trademark desalinization of a salinesolution, according to the of Ea tm K dak chem co in eton principle ofreverse osmosis, allows one to considerably In column 9 of Table 1 theflow rate of water is rereduce the concentration of salt dissolvedtherein. 75 corded, calculated for a film with a uniform thickness of 1micron. These values show that the higher permeability to water, P ofthe films of this invention, with the thickness remaining the same,enables one to obtain a flow rate of at least twice or more timesgreater than that which is obtained with a film of cellulose acetate.(The values given in column 9 were calculated by multiplying the valuesin column 3 by the values in column 5.)

The saline rejection data given in column 7 show that this property mayvary with the degree of substitution of the piperazine and with thenature of the dicarboxylic acid. In general the saline rejection is veryhigh, in some cases being even greater than that for cellulose acetate.

EXAMPLE 2 This example shows that with a decrease in thickness of thefilm there is an increase in the flow rate of produced water.

A poly(piperazinisophthalamide) film, prepared according to theprocedure described in Example 1(A), and having a thickness of microns,was placed in a cell for standard reverse osmosis. An aqueous salinesolution containing 5000 p.p.m. of NaCl was used as the feed. The linearflow rate of the feed on the surface of the film was 100' cm./sec., andthe operational pressure was 80 atmospheres.

The solution passing through the film contained 100 p.p.m. of NaCl,while the flow rate of water was about 42 liters per day per squaremeter of film surface.

A second film of poly(piperazinisophthalamide), pre pared as describedin Example 1(A), with a thickness of 43 microns, was placed in a cellfor standard reverse osmosis under the same conditions of the previousfilm.

The solution passing through the film contained 85 p.p.m. of CaCl Theflow rate of water was 4.1 liters per day per square meter of filmsurface.

EXAMPLE 3 A poly(trans 2,5 dimethylpiperazinadipamide) film, prepared asdescribed in Example 1(A), and having a thickness of 25 microns, wasplaced in a cell for standard reverse osmosis. An aqueous salinesolution containing 10,000 p.p.m. of MgSO was used as the feed. Thelinear flow rate of the feed on the film surface was 100 cm./sec. andthe operational pressure was 80 atmospheres.

The solution that passed through the film contained less than 50 p.p.m.of MgSO while the flow rate of water was about 14 liters per day squaremeter of film surface.

EXAMPLE 4 A film prepared according to Example 1(A) and consisting of ablend of poly(hexamethylenadipamide) (50 parts) andpoly(piperazinisophthalamide) (50 parts), and having a thickness of 46microns, was placed in a cell for standard reverse osmosis.

An aqueous saline solution containing 5000 p.p.m. of NaCl was used asthe feed. The linear flow rate of the feed on the film surface was 100cm./sec. and the operational pressure was 80 atmospheres.

The solution that passed through the film contained 845 p.p.m. of NaCl,while the flow rate of water was 6.7 liters per day per square meter offilm surface.

EXAMPLE 5 A gel type membrane was prepared according to the followingprocedure.

A solution was prepared which contained 15 g. of poly-(piperazinisophthalamide), 15 f. of formamide, and g. of 98% formicacid. This solution was then spread over a glass plate maintained at atemperature of 40 C. The film-spreader was regulated so as to form afilm with a thickness of about 200 microns. The film thus formed wasmaintained for 5 minutes at 40 C. During this time partial evaporationof the solvent took place. The film was then immersed into water and icefor a few hours. After removal from the glass plate, the film was thenkept in thewater until its use. This film had a thickness of 150 micronsand a water content of 63%.

The film or membrane was then put in a reverse osmosis cell of standardtype. A solution containing 10,000 p.p.m. of NaCl was used as the feed.The linear flow rate of the feed on the film surface was 100 cm./sec.and the operational pressure was atmospheres. A flow rate ofde-salinized water of liters/m. day with saline rejection of 77% wasobtained.

Variations can, of course, be made without departing from the spirit ofour invention. Having thus described our invention what we desire tosecure by Letters Patent and hereby claim is:

- What is claimed is:

1. In a reverse osmosis process for separating solute from solventcomprising disposing a solution of said solute in said solvent on oneside of a semi-permeable membrane and disposing said solvent on theother side thereof, said membrane permitting passage therethrough ofsaid solvent but not said solute, and applying a hydraulic pressureagainst said solution and said membrane, said pressure being greaterthan the osmotic pressure of said solution, an improvement comprisingemploying as said membrane a blend of at least two Synthetic polyamidesselected from the group consisting of poly (piperazinisophthalamide),poly-(trans 2,5-dimethyl piperazinterephthalamide), andpoly-(trans-2,5-dimethyl piperazin-trans-trans-muconamide) 2. In areverse osmosis process for separating solute from solvent comprisingdisposing a solution of said solute in said solvent on one side of asemi-permeable membrane and disposing said solvent on the other sidethereof, said membrane permitting passage therethrough of said solventbut not said solute, and applying a hydraulic pressure against saidsolution and said membrane, said pressure being greater than the osmoticpressure of said solution, an improvement comprising employing as saidmembrane, a blend of at least one synthetic polyamide selected from thegroup consisting of poly(piperazinisophthalamide),poly-(trans-2,5-dimethy1 piperazinterephthalamide), andpoly(trans-2,5-dimethyl piperazintrans-trans-muconamide), and a memberselected from the group consisting of nylon 6, nylon 4, nylon 6.6 andnylon 6.10.

References Cited UNITED STATES PATENTS 10/ 1972 Credali et al. 210-232/1970 Hoehn et al 210-321 X US. or X.R. 210 s0o age UNITED STATESPATENT OFFICE CERTIFICATE OF CO-RRECTIQN Patent No. 3,743,597 Dated July3, 1973 Inventofls) Lino Credali and Paolo Parrini It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 10: "l9,3 l8/69" should read 19,318 A/69 Columns 5-6Table 1, Column (5) "day/mi) should read day/m Columns 5-6, Table 1,Column (9) "(liters/day/day/m should read (liters/day/m Column 8, line2: "15 f." should read 15 g.

Signed and sealed this 26th day of March 197b,.

(SEAL) Attest:

EDWARD IVLFLETCHER,JR. G- MARSHALL DANN Attesting Officer Commissionerof Patents

